1. Field of the Invention
The present invention relates to a secondary battery. More particularly, the present invention relates to a structure promoting venting formed in a wide side of a can to form a vent deformation accelerator that is thinner than other parts in a cap plate, a bottom area of a can, or a narrow side of a can.
2. Description of the Related Art
Generally, contrary to a primary battery that is impossible to charge, a secondary battery can be charged or discharged so that it is widely used in high tech electronic applications, such as cellular phones, laptop computers, and camcorders. Especially, a lithium secondary battery has 3.6V driving voltage that is three times higher than that of a nickel-cadmium battery or a nickel-metal hydride and is used to power electronic equipment and has a high energy density per unit weight.
The lithium secondary battery mainly uses a lithium oxide as a cathode electrode active material and uses a carbon material as a anode electrode active material. Also, a lithium secondary battery is produced in various forms, such as cylinder shaped, square shaped, and pouch shaped.
A square shaped battery includes an electrode assembly, a can containing this electrode assembly, and a cap assembly combining with this can.
An electrode assembly separator separates the cathode and anode electrode and is arranged between these two electrodes, a cathode electrode and a anode tap respectively extend out from the cathode and anode electrodes.
A can is a container of metal material, having a rectangular parallelepiped shape in a square shaped secondary battery, is formed by deep drawing. A can may form a terminal of the battery. The can material can be a suitable aluminum alloy or aluminum that are high conductivity light weight metal materials. The can serves as the container of an electrode assembly and an electrolyte, and has an open upper part to allow insertion of the electrode assembly and is sealed by a cap assembly.
The cap assembly includes a cap plate attached to the upper part of the can, an electrode terminal passing through a terminal opening and having a gasket to insulate it from the cap plate, an insulation plate arranged on a lower side of a cap plate, and a terminal plate arranged on a lower side of an insulation plate and supplying an electric current to an electrode terminal. One electrode of the electrode assembly connects to the electrode terminal electrically through an electrode tap and the terminal plate and another electrode is electrically connected to the cap plate or can through a connecting electrode tap.
On the other hand, a vent can be formed on one side of a cap plate or on one edge of a wide part of the can. This vent ensures safety of a battery by discharging an internal gas because of preferentially opening, that is separating from the can, when the internal pressure of the battery is increased through overcharging.
However, some problems of such a vent are as follows.
First of all, a vent formed in a cap plate is a thinner part of a cap plate, the thickness of the edge of the vent where one can expect separating when the internal pressure of the battery is increased through overcharging is only a number of micrometers. Accordingly, designing a secondary battery that includes a vent operating at a lower pressure than the operating pressure of existing vents has a limitation. Also, there are some problems such as requiring accurate forming operations, increasing manufacturing costs, and delaying processing time to form a vent of minute thickness. Also, when an internal pressure is increased when changing the form of the can, there are disadvantages in that it cannot ensure safety of the can effectively because it can not handle a changing pressure of an internal part of the can.
On the other hand, a vent formed in a edge of the wide part of a can is a part that is formed to contain a groove of regular depth in a shape of an open-loop of a circle, a thickness of the vent where one can expect a change when the battery has a problem of is only several tens of micrometers. Therefore, a secondary battery including a vent that operates at a lower pressure than operating pressures of existing vents has a limitation as to design. Also, to form the vent to have an accurate thickness, there are some problems such as requiring accurate forming operations, increasing manufacturing costs, and delaying processing time.